[1000mp] Frequency Drift - ARGO measurement

[Tod - Minnesota]

Gary:

I am responding to you directly and also via the reflector so my answer can
reach some others as well. Gary's message to me follows my response.

Here is my comment to Gary:

My apologies to those on the reflector who might have tested the ARGO
program as Gary seems to have done. I happen to be in Minnesota for the next
several weeks and my FT1000MP is back in Idaho. That accounts for me
forgetting whether something should be USB or LSB as well as having
forgotten that prior to doing the frequency measurements I went into the
menus and set the non-transmit offsets to zero so that there would be no
chance that some tweaking of the frequencies done by the CPU would produce
errors in my readings. One of the Menu settings I changed was in group 8 and
the other was in Group 9. In both cases I wrote down the values that were
originally set in the menu. The changes I made were to set the RX-LSB and
RX-USB offsets to zero. After the measuring and the modification to the ref
osc board I restored the original offset values.

Gary comments that he can hear a difference in 'tone' between LSB and USB.
My note on doing the measuring indicated that unless the ref oscillator
frequency is set exactly where it should be there will be two different
frequencies measured by ARGO. One of these will be less than 500 Hz and the
other greater than 500 Hz. Most folks will be able to hear this difference
very easily. There is a trimmer on the ref oscillator board (TC4701) and if
you adjust the trimmer (very small amounts please) you will hear the tones
get further apart or closer together. This is one way to move the reference
oscillator frequency very close to the desired value even though you do not
have a high precision counter. If you look at the ARGO values as you tune
the trimmer you should be able to see and hear when you are within 2 Hz of
the 500 Hz values for the LSB and USB readings that confirm the oscillator
is set to the correct frequency. If the radio has not warmed up sufficiently
there will be drift off that point. In the case of my radio, the initial
frequencies were 410 Hz and 690 Hz. This gave me an estimate of 50 HZ off
frequency (410+690=1100. 1100/2 =550. 550-500 = 50Hz). As I tuned the
trimmer to the correct frequency the frequencies became symmetrically
positioned above and below 500 Hz and converged on 500 Hz. Once I had
adjusted the trimmer to get the correct ref osc frequency I was able to look
at the change of freq as a function of time following power on. The initial
power on frequencies were more than 75 Hz from the desired value, but they
were symmetrical in that one was 575Hz and the other 425Hz and they slowly
converged toward each being 500 Hz. The rate of change seemed to be about 3
Hz per minute slowing to 2 Hz and then 1.5 Hz per minute. After 45 minutes
the radio was still drifting slowly toward the desired frequency as the ref
oscillator crystal slowly warmed up.

For those folks who wish to tweak the ref oscillator trimmer, you will need
to remove both the top and bottom covers of the FT1000MP. On the right hand
side (as viewed from the front panel) at the very front of the side mounted
boards, is the reference oscillator and the trimmer, TC4701. A picture of
the reference oscillator board in its normal position in the radio is at
www.k0to.us  . Go to the JPG links following the home page picture and
select DSCN4434.jpg . That picture will show the trimmer at the bottom of
the board next to the crystal .



Tod, K�TO




-----Original Message-----
From: Gary Ferdinand W2CS [mailto:w2cs@bellsouth.net]
Sent: Sunday, March 30, 2003 9:14 AM
To: tao@skypoint.com
Subject: RE: [1000mp] Frequency Drift - ARGO measurement


Hi Tod,

Your setup of the two offsets on LSB and USB is something I've never thought
of doing before.  Interesting idea.  My ear at least seems to be more
capable of detecting tone differences than a beat note of 0 Hz!

Are there any aspects though that can make this compare invalid?  With the
"true zero beat" method you are using one rig configuration, presumably the
one used most, to determine if the rig's readout is on frequency.  With your
method you have introduced some variables such as the LSB/USB different
setting.  If one or both of those L(U)SB offsets were wrong, might you not
end up tweaking the ref osc when in fact it would be something else that
needed tweaking?

For example on my rig there seems to be a very slight difference in the
pitch of the noise depending on whether I listen (on CW) to the USB or the
LSB CW setting.  I've always written that off as asymmetric filter
characteristics, but perhaps my rig is misaligned in either USB or LSB. Or
is the carrier freq not touched one bit in the switch between USB and LSB -
perhaps not, as I think about it, since we're just looking at one SSB filter
vs another. Hmm. Perhaps I worry about nothing valid :-)

I appreciate any insight you might have.  BTW, I do *not* have the service
manual, only what is available onthe VA3CR web site. And, reading the Yaesu
schematics requires 20/5 eyesight!!

73,

Gary W2CS
Apex, NC



> 5. Switch back and forth between VFO A and VFO B. If your ref
> oscillator is
> set for the correct frequency the tone will be the SAME no matter
> which VFO
> you are listening to. (If the tones are different, your reference
> oscillator
> is not on the desired reference frequency.)
>
>